SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I know this has been hashed about before. Very useful advice in thread: Leaking Weathermatic 12000 valves
My situation: The whole system was installed in May of 2009. New house after fire in San Diego in 2007. Excellent Hunter controller controlling(what I percieve) are 18x one inch marginally designed Weathermatic 12000 valves. These valves are supposedly rated at 150psi(I think that's the explosion pressure). Sorry so negative, but I've had to clean and replace the diaphrams in most all of them every 12 to 18 months.
The static pressure in the system is 100 PSI. ALl of the valves and feed lines are 1". The flow rate is 12.16 GPM. The pressure and flow rate should be within the valve specs. The valves are all in boxes and eventually flood. The valves eventually leak between the 4 hold down screws. Tightening the screws does not help. Removing the tops shows the diaphrams coated with a slimey, greasy white film and usually, some fine grit sand. The valves all have upstream filters, which when inspected, have never even needed cleaning. The contamination has to be a result of the hammering as the valves close. Once the valves loosen to the point of leaking, I believe the sudden shutoff of the valve first forces water out the seams, and(I'm guessing) the sudden stoppage of flow sucks contaminants through the loosened seam back into the valve body.
I have DIG battery valves controlling microsprinklers(much less flow, but same pressure) and Rainbird 1" valves controlling rotary sprinklers with the same characteristics as the Weathermatic circuits. I've never had any issues with the DIGs or Rainbirds. These valves all have 6-8 cap screws, instead of the four corner arrangement on the Weathermatics(I'm guessing this was design by accountant)...
Soooo, that brings me to ask if any of the true experts in the forum have any suggestions. My inclination right now is to replace the valves with a better cap design. Replacing all 18 in a mature landscape won't be fun, but I'm getting furiously tired of "playing" with these leaky Weathermatics. Are there any valve suggetsions for replacement, if that would be the best course of action?
Thanks much,
MikeC(Discouraged and disgusted in San Diego)

Thanks .. Can you tell me why? I've not used a master valve before. Will it limit the hammering to the downstream valves or???

Thanks all. I'll have to evaluate the difficulty of putting in a MV. Reaching a point of the feed line before all valves is a minimum 250 ft run, hilly and accross at least one "farm" road. Added to that is the need to enclose all wiring in gopher proof shielding(pvc pipe). I suspect that's what I'll try first...
Any suggestions for a good choice of valve to use as a master?? What about brass vs. plastic?
Thanks again,
MikeC

I'll look into Weathermatic brass. I did forget to mention there already is a brass pressure regulator. It's around 450' from the valves to the pressure regilator. I may just put the master valve just behind the PV. Once past the 250' mark, the last 200' is an easy, flat slope. Having the PV & MV in one spot would prolly be a good thing.
I'm definitely a fan of unions. That's my one big gripe about my installer's valve installs.. No unions. I over torqued one of the bolts on a Weathermatic valve top and the brass insert turned in the plastic frame. Twas a pain to replace that valve body..
Great to have this forum.
-MikeC